[Etching] To form micropatterns, such as a semiconductor device, on a wafer, an etching process is carried out in such a way that a gas is ionized and dissociated using plasma to cause a dissociated substance to act on a wafer (react on the wafer surface) and remove a substance from the wafer. Ionized and dissociated substances vary and substances reacting therewith on the wafer also vary depending on product functions. To form a pattern on the wafer, the wafer is coated with a resist made of an organic-based substance and is subjected to photolithography to form a pattern on the wafer, then, the wafer is etched. To obtain a given pattern, a substance for adjusting reaction speed is introduced. In a chamber where the etching process is in progress, a variety of substances react with each other. It is described in Non-Patent Document 1 that etching performance, such as the size and selectivity of an etching rate, is determined depending on how various substance react with each other.
[OES] As ionization and dissociation caused by plasma accompanies optical emission phenomena, an etching apparatus that carries out plasma-utilized processing is equipped with an OES (Optical Emission Spectrometry) serving as an optical emission sensor to monitor the condition of a generation of plasma (Optical Emission Spectroscopy).
FIG. 1 illustrates optical emission data obtained by the OES (OES data mainly indicative of the relation between an optical emission spectrum and a waveform). An optical emission intensity spectrum distribution plotted on a graph with the horizontal axis representing time and the vertical axis representing wavelength is expressed as bit maps 101 to 103 (OES data bit maps). These bit maps graphically illustrate optical emission phenomena on a plurality of wafers (in the form of a light-and-shade scale of optical emission intensity). An optical emission intensity spectrum (optical emission spectrum) 111 at a certain time point indicates that the optical emission intensity is convex in a large area near the center of a monitored wavelength and that peaks appear at many wavelength positions. It is also observed that optical emission intensities along a process time sequence at specific wavelengths, that is, optical emission intensities during the etching process at wavelengths 121 and 122 change as the process goes on, and that, as indicated by a line a in the bit map 101, an optical emission phenomenon changes when the process contents is changed.
By monitoring such plasma-caused optical emission phenomena, etching process performance can be checked. For example, in high-volume manufacturing, optical emissions is monitored during consecutive processing of wafers to detect any abnormality. Optical emission data is also utilized as data for end-portion detection for determining a point of the end of the etching process. Optical emission monitoring is utilized because an optical emission at a specific wavelength is observed in correspondence to a specific substance in the chamber. For example, a carbon molecule C2 emits light at wavelengths of 473.7 and 516.5 [nm], a silicon fluoride molecule SiF emits light at wavelengths of 334.6, 336.3, 436.8, 440.1, and 777.0 [nm], and a nitrogen molecule N2 emits light at wavelengths of 282.0, 330.9, 405.9, 580.4, and 607.0 [nm]. The same molecule shows different optical omission wavelengths depending on its different energy states. Peaks appear on the optical emission spectrum 111, depending on such optical emission wavelengths.
[Optical emission intensity] Etching is a chemical reaction. A certain substance (molecular composition) turns into a different substance (molecular composition). Transformations like this accompany a highly correlated phenomenon.
FIG. 2 depicts the cause of the correlation between optical emission intensities based on a reaction (relation between chemical reactions and waveforms). At a first-order chemical reaction 201, a substance [A] is decomposed into a substance [B] and a substance [C] and the process of this reaction is defined by an equation 202 (first-order chemical reaction speed). At a second-order chemical reaction 203, two substances [A] (2[A]) bond together to form the substance [C], the process of which is defined by an equation 204 (second-order chemical reaction speed). At a high-order chemical reaction 205 in which a number of substances ([A]+ . . . ) bond to form the substance [C], the process is defined by an equation 206 (high-order chemical reaction speed). These reactions indicate that the relation between an increase and a decrease of substances can be explained by one substance in each reaction. For example, at a reaction 211 in which a [substance 1] turns into a [substance 2] and a [substance 3] (chemical reaction), the correlation between waveforms appears, as shown in a graph below (where the horizontal axis represents time and the vertical axis represents optical emission intensity), such that the [substance 2] and [substance 3] increase in response to a decrease in the [substance 1]. In other words, a proportional relation of optical emission intensities results.
In high-volume manufacturing of semiconductor device wafers, wafers are processed in lots repeatedly by a single etching apparatus. A lot is a unit for processing a group of wafers. One lot consists of several to scores of wafers, which are etched consecutively in each of chambers incorporated in the etching apparatus.
FIG. 3 is a graph of a time-serves variation of optical emission intensities (non-controlled optical emission intensities) at individual wavelengths for each wafer in a lot-wafer etching process. Figures on the horizontal axis represents lot units (plotted for each wafer), and the vertical axis represents optical emission intensities plotted against individual wavelengths. The optical emission intensity changes to rise and fall for each wafer in a lot. Optical emission intensity variation is also observed between different lots. The optical emission intensity reflects how a chemical reaction proceeds, and this chemical reaction determines etching performance. Optical emission intensity variation for each lot and wafer, therefore, means the variation of the etching performance. To stabilize the etching performance and obtain constant etching results at high repetitive precision, etching process conditions must be adjusted. Hence various actuators (a plurality of actuator values) related to the flow rates of various gases affecting reactions, current and voltage by high-frequency (RF) power, the internal pressure of chamber, etc., are adjusted.
Japanese Patent Application Laid-Open Publication No. 2003-17471 (Patent Document 1) discloses an apparatus and a process method which predict a process result based on output from a sensor that monitors a processing volume during a process and adjust/manipulate process conditions so that the process result comes to coincide with a target value. Patent Document 1 particularly describes adjustment/manipulation of a plurality of recipe parameters.
Japanese Patent Application Laid-Open Publication No. 2003-158160 (Patent Document 2) discloses a technique of quantifying the quality of a measured film based on an infrared absorption spectrum measured by an FT-IR method (Fourier-transform Infrared Spectroscopy) and adjusting a film-forming temperature. At this time, particularly, a PLS regression analysis (Partial Least Square Regression or Projection to Latent Structure Regression) which is configured to take in correlational change of substances such as a chemical reaction to perform a regression analysis is used.
Japanese Patent Application Laid-Open Publication No. 2004-207703 (Patent Document 3) discloses a technique of setting process conditions for a processing apparatus in correspondence to a process result that is a measurement taken after the end of the process. Patent Document 3 particularly describes a technique of predicting a process result from operation data of a processing apparatus, such as OES, including sensor data and using the PLS regression analysis for making such a prediction.